Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide method and apparatus for video coding. In some examples, an apparatus includes processing circuitry. The processing circuitry decodes a first portion of video data to obtain first decoded data corresponding to at least two pictures of a plurality of pictures. The processing circuitry identifies one or more pictures of the at least two pictures for decoding a second portion of the video data corresponding to a current picture. In a case that the one or more identified pictures includes two or more identified pictures, the processing circuitry selects a collocated reference picture based on one of (i) the POC numbers of the two or more identified pictures and the current picture, and (ii) a selection index provided in the video data. The processing circuitry also decodes the second portion of the video data using the collocated reference picture.

INCORPORATION BY REFERENCE

The present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/695,377, “METHODS FOR STORING TEMPORALMOTION VECTORS IN MOTION COMPENSATION PREDICTION” filed on Jul. 9, 2018,which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding,” December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videocoding. In some examples, an apparatus includes processing circuitrythat decodes a first portion of video data to obtain first decoded datacorresponding to at least two pictures of a plurality of pictures, thevideo data corresponding to the plurality of pictures that is associatedwith respective Picture Order Count (POC) numbers indicating a temporalorder of the plurality of pictures and respectively in a plurality oftemporal layers. The processing circuitry identifies one or morepictures of the at least two pictures for decoding a second portion ofthe video data corresponding to a current picture. In a case that theone or more identified pictures includes two or more identifiedpictures, the processing circuitry selects a collocated referencepicture from the two or more identified pictures based on one of (i) thePOC numbers of the two or more identified pictures and the currentpicture, and (ii) a selection index provided in the video data, the twoor more identified pictures being in different temporal layers. In acase that the one or more identified pictures includes only oneidentified picture, the processing circuitry selects the only oneidentified picture as the collocated reference picture. The processingcircuitry also decodes the second portion of the video data using thecollocated reference picture to obtain second decoded data correspondingto the current picture.

In some examples, in the case that the one or more identified picturesincludes the two or more identified pictures, the processing circuitryselects one of the two or more identified pictures that corresponds to aclosest POC number difference with respect to the current picture as thecollocated reference picture.

In some examples, in the case that the one or more identified picturesincludes the two or more identified pictures, and in a case that two ofthe two or more identified pictures correspond to a closest POC numberdifference with respect to the current picture, the processing circuitryperforms one of selecting one of the two of the two or more identifiedpictures in a lowest temporal layer of the identified pictures as thecollocated reference picture, and selecting one of the two of the two ormore identified pictures in a highest temporal layer of the identifiedpictures as the collocated reference picture.

In some examples, the plurality of temporal layers includes N temporallayers, and the processing circuitry allocates M memory spacesassociated with M of the plurality of temporal layers, respectively, andstores the first decoded data corresponding to the one or moreidentified pictures in one or more respective memory spaces of the Mallocated memory spaces according to the temporal layer of each of theone or more identified pictures, where M is a positive integer rangingfrom two to N. In some examples, the processing circuitry obtains thepositive integer M from the video data. In some examples, the processingcircuitry determines the positive integer M based on a picture size ofthe plurality of pictures. In some embodiments, the positive integer Nis greater than two, the positive integer M is less than or equal to thepositive integer N, and the M allocated memory spaces are associatedwith M lower temporal layers among the N plurality of temporal layers.

In some examples, the plurality of temporal layers include N temporallayers, and the processing circuitry allocates M memory spaces, storesthe first decoded data corresponding to the one or more identifiedpictures in one or more respective memory spaces of the M allocatedmemory spaces, and, in a case that the one or more identified picturesincludes less than M pictures and the current picture is in a lowesttemporal layer of the temporal layers, stores the second decoded datacorresponding to the current picture in a vacant one of the M memoryspaces, where M is a positive integer less than or equal to N.

In some examples, in a case that the one or more identified picturesincludes a particular picture in a same temporal layer as the currentpicture, the processing circuitry stores the second decoded datacorresponding to the current picture in place of decoded datacorresponding to the particular picture. In some examples, in a casethat the one or more identified pictures includes a particular picturein a same temporal layer as the current picture, the processingcircuitry partially updates decoded data stored in one of the M memoryspaces that corresponds to the particular picture using the seconddecoded data corresponding to the current picture.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of a current block, its surroundingspatial candidates, and its collocated candidates in one example.

FIG. 9 is a schematic illustration of a plurality of pictures associatedwith respective Picture Order Count (POC) numbers in a plurality oftemporal layers in accordance with an embodiment.

FIG. 10 shows a flow chart outlining a decoding process (1000) accordingto an embodiment of the disclosure.

FIG. 11 shows a flow chart outlining an encoding process (1100)according to an embodiment of the disclosure.

FIG. 12 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers, and smartphones, but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230), and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks, and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs), andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

FIG. 8 is a schematic illustration of a current block (801), itssurrounding spatial candidates, and its collocated candidates in oneexample.

Referring to FIG. 8, the motion information of a current block (801) canbe derived based on the motion information of the surrounding blocks,denoted as surrounding spatial candidates A0, A1, and B0, B1, B2 (forblocks 802 through 806), respectively. Moreover, in some applications,the motion information of the current block (801) can be derived basedon the motion information of a predetermined collocated candidate (alsoreferred to as a temporal candidate). For example, the current block(801) may have a collocated block in a specified reference picture. Ifblock (812) of the specified reference picture that corresponds to aposition outside the current block and adjacent to a lower-right cornerof the current block (801) is coded using the inter-picture prediction,the block (812) is used as the collocated block and the motioninformation thereof is used as the collocated candidate (C0). However,if the block (812) is not coded using the inter-picture prediction,block (813) that corresponds to a position at the lower-right side of,and adjacent to, a center of the block (801) is used as the collocatedblock and the motion information thereof is used as the collocatedcandidate (C1). In some examples, at least one pruning operation can beperformed to ensure duplicated candidates are not included in acandidate list more than once.

In some video coding standards, after using spatial and temporal motioninformation of neighboring blocks to predict the motion information ofthe current block, the prediction residue is further coded. Such amethod is referred to in HEVC as Advanced Motion Vector Prediction(AMVP) mode.

In some examples, a two-candidate motion vector predictor list can beformed. The first candidate predictor is from the first available motionvector from the left edge, in the order of spatial A0, A1 candidates.The second candidate predictor is from the first available motion vectorfrom the top edge, in the order of spatial B0, B1 and B2 candidates. Ifno valid motion vector can be found from the checked locations foreither the left edge or the top edge, no candidate will be filled in thelist. If two candidates are determined to be available and are the same,only one will be kept in the list. If the list is not full (i.e., withtwo different candidates), the temporal collocated motion vector (afterscaling), e.g., collocated candidate (C0), can be used as anothercandidate. If candidate (C0) is not available, collocated candidate (C1)can be used instead. In some examples, if there are still not enoughmotion vector predictor candidates after checking the collocatedcandidates (C0) and (C1), a zero motion vector can be added to the list.

FIG. 9 is a schematic illustration of a plurality of pictures associatedwith respective Picture Order Count (POC) numbers in a plurality oftemporal layers in accordance with an embodiment.

In order to support temporal scalability, in some video codingconfigurations, the pictures in a sequence are encoded/decoded in areordered manner. For example, FIG. 9 shows a plurality of pictures (910through 918) in a group of pictures (GOP). The pictures are associatedwith respective POC numbers (POC=1 through 8) indicating a temporalorder of the pictures and respectively in a plurality of temporallayers. Each layer of the temporal layers is identified in FIG. 9 by arespective temporal ID (Tid). In some examples, when decoding, picturesin lower temporal layers (with smaller Tids) will be decoded prior todecoding picture in higher temporal layers (with larger Tids). Thereference pictures may be assigned to facilitate such decoding ordering.For example, a picture in a higher temporal layer can use pictures in alower temporal layer or pictures of the same temporal layer as referencepictures. However, a picture in a lower temporal layer cannot use apicture in a higher temporal layer as a reference picture.

In FIG. 9, picture (910) is associated with POC=0 and is in a temporallayer with Tid=0; picture (911) is associated with POC=1 and is in atemporal layer with Tid=3; picture (912) is associated with POC=2 and isin a temporal layer with Tid=2; picture (913) is associated with POC=3and is in the temporal layer with Tid=3; picture (914) is associatedwith POC=4 and is in the temporal layer with Tid=1; picture (915) isassociated with POC=5 and is in the temporal layer with Tid=3; picture(916) is associated with POC=6 and is in the temporal layer with Tid=2;picture (917) is associated with POC=7 and is in the temporal layer withTid=3; and picture (918) is associated with POC=8 and is in the temporallayer with Tid=0. In some examples, pictures (910-918) can have adecoding order listed using the POC numbers thereof: 0, 8, 4, 2, 1, 3,6, 5, 7.

In some applications, such as deriving motion information using themerge mode or the AMVP mode, the temporal motion information, whichincludes motion vectors and other information (such as predictiondirection, reference index, etc.) for one or more previously decodedpictures (or also referred to as reference pictures), would be requiredto be stored such that when coding a block in a future picture, suchtemporal vectors can be used as a motion vector predictor.

In some coding methods, a slice header flag is used to specify which oneof the reference pictures is used for the current slice for deriving thetemporal motion vector predictors. This picture is referred as the“collocated reference picture.” In some coding methods, because anypreviously decoded picture can be assigned as the “collocated referencepicture” for decoding a current picture, all decoded pictures within theslice and associated motion information are all stored in a decodedpicture buffer.

In a video coding system, for each reference picture stored in thedecoded picture buffer, a picture-size memory space is allocated tostore the image samples of the reference picture. At the same time,another memory space (also called a motion information memory space)associated with this picture-size memory space is also allocated tostore the motion vectors and other motion information in this picture.To store K reference pictures, K picture-size memory spaces and K motioninformation memory spaces are required. Reducing the number of referencepictures that need to be stored can reduce the required memory spacesand improve memory channel bandwidth efficiency.

In some embodiments, the reference pictures that can be assigned as acollocated reference picture for a current picture is limited to at mostone decoded picture for each temporal layer. In some examples, thenumber of total motion information memory spaces needed is decided bythe number of temporal layers in the coding structure. In some examples,when the pictures in the highest temporal layer cannot be used as areference picture, the amount of total motion vector (and motioninformation) memory space needed is decided by the number of temporallayers in the coding structure minus 1. In some examples, for picturesof each temporal layer, the motion information memory space can storethe motion vector and other motion information of the most recentlyencoded/decoded picture in this temporal layer.

Using the GOP shown in FIG. 9 as an example, the pictures are arrangedinto a four-temporal-layer structure. For each layer, a motioninformation memory space is allocated and assigned to store temporalmotion vectors and motion information for the most recentlyencoded/decoded picture of this layer. As shown in Table I, theavailable collocated reference picture(s) for each picture (in decodingorder) varies as the decoding process progresses.

TABLE I Available collocated reference picture according to temporallayers Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 2 1 3 6 5 7 POCTid 0 0 1 2 3 3 2 3 3 Available — 0 8 4, 2, 2, 2, 4, 4, Collocated 8 4,4, 4, 6, 6, POC 8 8 8 8 8

As shown in Table I, after picture (910) (POC=0, Decoding Order=0) isdecoded, the motion information memory space associated with temporallayer (Tid=0) will store the motion information associated with thispicture (910) for decoding the next picture (918). After picture (918)(POC=8, Decoding Order=1) is decoded, the motion information memoryspace associated with temporal layer (Tid=0) will store the motioninformation associated with this picture (918) in place of the motioninformation of the picture (910) for decoding the next picture (914).After picture (914) (POC=4, Decoding Order=2) is decoded, the motioninformation memory space associated with (Tid=1) will store the motioninformation associated with this picture (914). Therefore, for decodingpicture (912), motion information of pictures (918) and (914) may bestored and selectable.

After picture (912) (POC=2, Decoding Order=3) is decoded, the motioninformation memory space associated with (Tid=2) will store the motioninformation associated with this picture (912). After picture (916)(POC=6, Decoding Order=6) is decoded, the motion information memoryspace information memory space (Tid=2) will be updated with the motioninformation associated with this picture (916). If the pictures in thetemporal layer (Tid=3), such as pictures (911, 913, 915, and 917) can beused as reference pictures, a motion information memory space for thetemporal layer (Tid=3) will also be allocated and assigned and updatedaccordingly.

In Table I, for decoding some pictures, such as picture (916) (POC=6),more than one reference picture may qualify to be used as the collocatedreference picture, such as pictures (912), (914), and (918) (POC=2, 4,8). The choice of collocated reference picture may be signaled usingcontrol information included in the encoded video data, or derived basedon information such as a POC difference and/or temporal layerrelationship.

In one example, the collocated reference picture is selected based on aselection index provided in the video data.

In some examples, the one of the available reference pictures thatcorresponds to a closest POC number difference with respect to thecurrent picture is selected as the collocated reference picture.

In some examples, when in a case that the available reference picturesinclude two pictures with a same closest POC number difference withrespect to the current picture, the one of the two pictures in a lowertemporal layer of the two pictures can be selected as the collocatedreference picture (as shown in Table II), or the one of the two picturesin a higher temporal layer of the two pictures can be selected as thecollocated reference picture (as shown in Table III).

TABLE II Collocated picture selection according to POC difference andhigher temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 8 4 2 2 4 4 6 picturePOC

TABLE III Collocated picture selection according to POC difference andlower temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 8 4 2 4 8 6 8 picturePOC

In some embodiments, the reference pictures that can be assigned as acollocated reference picture for a current picture is limited to at mosta maximum number M of decoded pictures, which may be in M lower temporallayers among the plurality of temporal layers. In some examples, thenumber of total motion information memory spaces needed is decided bythe number of temporal layers in the coding structure and a buffer sizethreshold. Also, in some examples, the number of total motioninformation memory spaces needed is capped by a threshold whichspecifies the maximum allowed buffer size. For example, if the number oftemporal layers is N and the buffer size threshold determines that amaximum number of motion information memory spaces for differenttemporal layers is M, where M is a positive integer equal to or lessthan N, then only the pictures in the lower M temporal layers will beassociated with a respective motion information memory space. In someexamples, for pictures of each temporal layer, the motion informationmemory space can store the motion vector and other motion information ofthe most recently encoded/decoded picture in this temporal layer.

In one embodiment, the maximum number of motion information memoryspaces (e.g., the positive integer M) can be determined based on apicture size of the plurality of pictures. In some examples, comparedwith a set of higher resolution pictures, the maximum number of motioninformation memory spaces for a set of lower resolution pictures can beset at a greater number.

In another embodiment, the maximum number of motion information memoryspaces (e.g., the positive integer M) can be determined based on amaximum supported picture resolution. In some examples, when the decoderis set to process pictures at a lower resolution, compared withprocessing the pictures at a higher, default, resolution, the maximumnumber of motion information memory spaces can be set at a greaternumber.

Using the GOP shown in FIG. 9 as an example, the pictures are arrangedinto a four-temporal-layer structure. For each layer, a motioninformation memory space is allocated and assigned to store temporalmotion vectors and motion information for the most recentlyencoded/decoded picture of this layer. Also, in some examples, if themaximum allowed motion information memory spaces is set to two, onlypictures in the temporal layers (Tid=0) and (Tid=1) will be used asavailable collocated reference pictures. As shown in Table IV, theavailable collocated reference picture(s) for each picture (in decodingorder) varies as the decoding process progresses.

TABLE IV Available collocated reference picture according to M = 2 lowertemporal layers Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 2 1 3 65 7 POC Tid 0 0 1 2 3 3 2 3 3 Available — 0 8 4, 4, 4, 4, 4, 4,Collocated 8 8 8 8 8 8 POC

As shown in Table IV, after picture (918) (POC=8, Decoding Order=1) isdecoded, the motion information memory space associated with temporallayer (Tid=0) will store the motion information associated with thispicture (918) for decoding the next picture (914). After picture (914)(POC=4, Decoding Order=2) is decoded, the motion information memoryspace associated with (Tid=1) will store the motion informationassociated with this picture (914). In this example, for allsubsequently decoded pictures with Tid greater than one, the motioninformation memory spaces will not be updated and the motion informationcorresponding to pictures (918) and (914) will remain as the availablecollocated reference pictures.

In Table IV, for decoding some pictures, pictures (912), (911), (913),(916), (915), and (917) (POC=2, 1, 3, 6, 5, 7) may have more than oneavailable collocated reference picture, such as pictures (914) and (918)(POC=4, 8). The choice of collocated reference picture may be signaledusing control information included in the encoded video data, or derivedbased on information such as a POC difference and/or temporal layerrelationship.

In one example, the collocated reference picture is selected based on aselection index provided in the video data.

In some examples, the one of the available reference pictures thatcorresponds to a closest POC number difference with respect to thecurrent picture is selected as the collocated reference picture.

In some examples, when the available reference pictures include twopictures with a same closest POC number difference with respect to thecurrent picture, the one of the two pictures in a lower temporal layerof the two pictures can be selected as the collocated reference picture(as shown in Table V), or the one of the two pictures in a highertemporal layer of the two pictures can be selected as the collocatedreference picture (as shown in Table VI). See, for example, the columnsfor decoding picture (916) (POC=6) in Table V and Table VI.

TABLE V Collocated picture selection according to POC difference andhigher temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 8 4 4 4 4 4 8 picturePOC

TABLE VI Collocated picture selection according to POC difference andlower temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 8 4 4 4 8 4 8 picturePOC

In some other embodiments, when the selection of the collocated pictureis specified at a slice level for corresponding slices, there is no needto signal the selection of collocated picture at a picture level.

In some embodiments, the reference pictures that can be assigned as acollocated reference picture for a current picture is limited to at mosta maximum number M of decoded pictures, which may be in M lower temporallayers among the plurality of temporal layers, where the motioninformation of two pictures in a lowest temporal layer of the temporallayers may be concurrently stored in a case that not all M allocatedmotion information memory spaces are occupied.

In some examples, the number of temporal layers is N and the buffer sizethreshold determines that a maximum number of motion information memoryspaces for different temporal layers is M, where M is a positive integerequal to or less than N. When the number of decoded pictures havingdecoded data stored in the motion information memory spaces is less thanM (i.e., the allocated motion information memory spaces are not alloccupied by decoded data of respective pictures), the motion informationof a decoded picture in the lowest temporal layer of the temporal layersis allowed to be stored in a vacant motion information memory space,even when the motion information of another picture in the lowesttemporal layer has already been stored in one of the allocated motioninformation memory spaces. However, when the number of decoded pictureshaving decoded data stored in the motion information memory spaces is M(i.e., the allocated motion information memory spaces are all occupiedby decoded data of respective pictures), the stored pictures and thecurrently decoded picture are in different temporal layers, and thestored pictures include two pictures in the lowest temporal layer, thedecoded data of the currently decoded picture can still be stored but inone of the two motion information memory spaces that is occupied by oneof the two pictures in the lowest temporal layer that has a smallest POCnumber. Afterwards, the motion information stored in the M motioninformation memory spaces will correspond to M pictures in M differenttemporal layers.

Using the GOP shown in FIG. 9 as an example, the pictures are arrangedinto a four-temporal-layer structure, where M is set to three. As shownin Table VII, the available collocated reference picture(s) for eachpicture (in decoding order) varies as the decoding process progresses.

TABLE VII Available collocated reference picture according to temporallayers Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 2 1 3 6 5 7 POCTid 0 0 1 2 3 3 2 3 3 Available — 0 0, 0, 2, 2, 2, 4, 4, Collocated 8 4,4, 4, 4, 6, 6, POC 8 8 8 8 8 8

As shown in Table VII, after picture (910) (POC=0, Decoding Order=0) isdecoded, the motion information associated with this picture (910) isstored in one of M memory spaces for decoding the next picture (918).After picture (918) (POC=8, Decoding Order=1) is decoded, because atleast one vacant memory space is available, the motion informationassociated with this picture (918) is stored in another one of the Mmemory spaces for decoding the next picture (914) without clearing thestored motion information associated with picture (910). At this stage,motion information of two pictures in the lowest temporal layer isstored in the motion information memory spaces. After picture (914)(POC=4, Decoding Order=2) is decoded, because one vacant memory space isstill available, the motion information associated with this picture(914) is stored in yet another one of the M memory spaces for decodingthe next picture (912) without clearing the stored motion informationassociated with pictures (910) and (918). Therefore, for decodingpicture (912), motion information of pictures (910), (918), and (914)may be stored and selectable.

After picture (912) (POC=2, Decoding Order=3) is decoded, the motioninformation associated with this picture (912) will be stored to updatethe motion information associated with picture (910), which has thelowest POC among the stored pictures in the lowest temporal layer.

In some embodiments, various approaches are applicable to update storedmotion information associated with a particular temporal layer.

In some examples, the stored motion information can be replaced in apicture-wise manner. For example, in a case that the stored motioninformation of a particular picture and a currently decoded picture arein a same temporal layer, the motion information of the currentlydecoded picture is stored in place of the motion information ofparticular picture. Using Table VII as an example, after picture (912)(POC=2, Decoding Order=3) is decoded, the entirety of stored motioninformation associated with picture (910) (POC=0) is deleted andreplaced with the motion information associated with picture (912)(POC=2).

In some other examples, the stored motion information can be replaced ina block-wise manner. For example, in a case that the stored motioninformation of a particular picture and a currently decoded picture arein a same temporal layer, the stored motion information of particularpicture can be partially updated by the motion information of thecurrently decoded picture. Using Table VII as an example, after picture(912) (POC=2, Decoding Order=3) is decoded, the stored motioninformation associated with picture (910) (POC=0) is updated by themotion information associated with picture (912) (POC=2). Specifically,in some examples, for each block, when a block of the picture (912)(POC=2) contains motion information, the motion information for acollocated block in the picture (910) (POC=0) is replaced by the motioninformation of this block of the picture (912) (POC=2). After all blocksin the picture (910) (POC=0) have been processed, the motion informationmemory space will be indicated as associated with the picture (912)(POC=2).

The choice of collocated reference picture may be signaled using controlinformation included in the encoded video data, or derived based oninformation such as a POC difference and/or temporal layer relationship.In one example, the collocated reference picture is selected based on aselection index provided in the video data. In some examples, the one ofthe available reference pictures that corresponds to a closest POCnumber difference with respect to the current picture is selected as thecollocated reference picture.

In some examples, when the available reference pictures include twopictures with a same closest POC number difference with respect to thecurrent picture, the one of the two pictures in a lower temporal layerof the two pictures can be selected as the collocated reference picture(as shown in Table VIII), or the one of the two pictures in a highertemporal layer of the two pictures can be selected as the collocatedreference picture (as shown in Table IX).

TABLE VIII Collocated picture selection according to POC difference andhigher temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 0 0 2 2 4 4 6 picturePOC

TABLE IX Collocated picture selection according to POC difference andlower temporal layer Decoding Order 0 1 2 3 4 5 6 7 8 “Current” 0 8 4 21 3 6 5 7 POC Tid 0 0 1 2 3 3 2 3 3 Collocated — 0 0 4 2 4 8 6 8 picturePOC

FIG. 10 shows a flow chart outlining a decoding process (1000) accordingto an embodiment of the disclosure. The process (1000) can be used inthe reconstruction of a plurality of pictures, such as a GOP, havingblocks coded in inter mode. In some embodiments, one or more operationsmay be performed before or after process (1000), and some of theoperations illustrated in FIG. 10 may be reordered or omitted.

In various embodiments, the process (1000) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video decoder (310), (410), or (710), and the like. Insome embodiments, the process (1000) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1000). Theprocess starts at (S1001) and proceeds to (S1010).

At (S1010), a first portion of video data is decoded to obtain firstdecoded data corresponding to at least two pictures of a plurality ofpictures (e.g., GOP). In some examples, the video data corresponding tothe plurality of pictures is associated with respective Picture OrderCount (POC) numbers indicating a temporal order of the plurality ofpictures and respectively in a plurality of temporal layers, asillustrated with reference to FIG. 9. For example, as shown in Table I,after decoding at least pictures (910) and (918) (POC=0.8), a portion ofvideo data is decoded to obtain decoded data, including motioninformation, that corresponds to the decoded pictures. In some examples,the first portion of video data can be decoded using the system ordecoders illustrated with reference to FIGS. 3, 4, and 7.

At (S1020), one or more pictures of the at least two pictures areidentified for decoding a second portion of the video data correspondingto a current picture. For example, based on the rules illustrated withreference to Table I, Table IV, and Table VII, at different stages ofdecoding a GOP, one or more pictures that can be used as availablecollocated reference pictures are identified.

In some embodiments, the plurality of temporal layers includes Ntemporal layers. Before performing (S1020), M memory spaces associatedwith M of the plurality of temporal layers can be allocated,respectively, where M is a positive integer less than or equal to N, orin some examples ranging from two to N. In some examples, the firstdecoded data corresponding to the one or more identified pictures can bestored in one or more respective memory spaces of the M allocated memoryspaces according to the temporal layer of each of the one or moreidentified pictures.

In some examples, the positive integer M can be obtained from the videodata. In some examples, the positive integer M can be determined basedon a picture size of the plurality of pictures.

In some embodiments, the positive integer N is greater than two, thepositive integer M is less than or equal to the positive integer N, andthe M allocated memory spaces are associated with M lower temporallayers among the N plurality of temporal layers.

At (S1030), a collocated reference picture is selected from the one ormore identified pictures. In some examples, in a case that the one ormore identified pictures includes two or more identified pictures, acollocated reference picture can be selected from the two or moreidentified pictures based on one of (i) the POC numbers of the two ormore identified pictures and the current picture, and (ii) a selectionindex provided in the video data. The two or more identified picturesare in different temporal layers. In some other examples, in a case thatthe one or more identified pictures includes only one identifiedpicture, the only one identified picture can be selected as thecollocated reference picture.

In some examples, one of the two or more identified pictures with aclosest POC number difference with respect to the current picture can beselected as the collocated reference picture. In some examples, in acase that there are two of the two or more identified pictures with aclosest POC number difference with respect to the current picture, thecollocated reference picture can be selected from these two picturescorresponding to the same POC number difference by either (i) selectingone of the two of the two or more identified pictures in a lowesttemporal layer of the identified pictures as the collocated referencepicture, or (ii) selecting one of the two of the two or more identifiedpictures in a highest temporal layer of the identified pictures as thecollocated reference picture, as similarly illustrated with reference toTable II, Table III, Table V, Table VI, and Table VIII, and Table IX.

At (S1040), the second portion of the video data is decoded using theselected collocated reference picture to obtain second decoded datacorresponding to the current picture. In some examples, the secondportion of video data can be decoded using the system or decodersillustrated in FIGS. 3, 4, and 7.

At (S1050), in a case that all pictures in the GOP are decoded, theprocess proceeds to (S1099); and in a case that not all pictures in theGOP are decoded, the process proceeds to (S1020). With the newly decodeddata from (S1040) corresponding to the current picture, at (S1020),whether the current picture from (S1040) is included in the newlyidentified pictures for decoding a next picture is determined.

In some examples, in a case that the one or more previously identifiedpictures includes less than M pictures and the current picture is in alowest temporal layer of the temporal layers, the second decoded datacorresponding to the current picture is identified as an availablecollocated reference picture and is stored in a vacant one of the Mmemory spaces.

In some examples, in a case that the one or more previously identifiedpictures includes M pictures, the one or more previously identifiedpictures and the current picture are in different temporal layers, andthe one or more previously identified pictures includes two pictures inthe lowest temporal layer, the second decoded data corresponding to thecurrent picture is stored in one of the M memory spaces that storesdecoded data corresponding to one of the two pictures in the lowesttemporal layer that has a smallest POC number.

In some examples, in a case that the one or more previously identifiedpictures includes a particular picture in a same temporal layer as thecurrent picture, the second decoded data corresponding to the currentpicture is stored in place of decoded data corresponding to theparticular picture. In some alternative examples, in a case that the oneor more previously identified pictures includes a particular picture ina same temporal layer as the current picture, decoded data stored in oneof the M memory spaces that corresponds to the particular picture ispartially updated using the second decoded data corresponding to thecurrent picture.

At (S1099), the process for decoding the POC terminates.

FIG. 11 shows a flow chart outlining an encoding process (1100)according to an embodiment of the disclosure. The process (1100) can beused in encoding a plurality of pictures, such as a GOP, having blockscoded in inter mode. In some embodiments, one or more operations may beperformed before or after process (1100), and some of the operationsillustrated in FIG. 10 may be reordered or omitted.

In various embodiments, the process (1100) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video encoder (303), (503), or (603), and the like. Insome embodiments, the process (1100) is implemented in softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1100). Theprocess starts at (S1101) and proceeds to (S1110).

At (S1110), at least two pictures of a GOP are encoded as a firstportion of video data. In some examples, the GOP includes a plurality ofpictures that is associated with respective Picture Order Count (POC)numbers indicating a temporal order of the plurality of pictures andrespectively in a plurality of temporal layers, as illustrated withreference to FIG. 9. In some examples, the pictures can be encoded usingthe system or encoders illustrated in FIGS. 3, 5, and 6.

At (S1120), one or more pictures of the at least two pictures areidentified for encoding a current picture. For example, based on therules illustrated with reference to Table I, Table IV, and Table VII,and similarly illustrated with reference to (S1020), at different stagesof encoding a GOP, one or more pictures that can be used as availablecollocated reference pictures are identified.

At (S1130), a collocated reference picture is selected from the one ormore identified pictures. In some examples, in a case that the one ormore identified pictures includes two or more identified pictures, acollocated reference picture can be selected from the two or moreidentified pictures based on one of (i) the POC numbers of the two ormore identified pictures and the current picture, and (ii) evaluatingcoding complexity and/or efficiency of using different collocatedreference picture. In the scenario (i), the collocated reference picturecan be selected in a manner similar to various examples illustrated withreference to (S1030) and Table II, Table III, Table V, Table VI, andTable VIII, and Table IX. In the scenario (ii), the selected collocatedreference picture based on the coding complexity and/or efficiency is tobe provided as a selection index included in the encoded video data.

At (S1140), the current picture can be encoded as a second portion ofthe video data using the collocated reference picture. In some examples,the second portion of video data can be encoded using the system orencoders illustrated in FIGS. 3, 5, and 6.

At (S1150), in a case that all pictures in the GOP are encoded, theprocess proceeds to (S1199); and in a case that not all pictures in theGOP are encoded, the process proceeds to (S1120). After encoding thecurrent picture, at (S1120), whether the current picture from (S1140) isincluded in the newly identified pictures for decoding a next picture isdetermined in a manner similar to the examples as illustrated withreference to (S1150) and (S1120).

At (S1199), the process for encoding the POC terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 12 shows a computersystem (1200) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 12 for computer system (1200) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1200).

Computer system (1200) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1201), mouse (1202), trackpad (1203), touchscreen (1210), data-glove (not shown), joystick (1205), microphone(1206), scanner (1207), camera (1208).

Computer system (1200) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1210), data-glove (not shown), or joystick (1205), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1209), headphones(not depicted)), visual output devices (such as screens (1210) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1200) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1220) with CD/DVD or the like media (1221), thumb-drive (1222),removable hard drive or solid state drive (1223), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1200) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1249) (such as, for example USB ports of thecomputer system (1200)); others are commonly integrated into the core ofthe computer system (1200) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1200) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1240) of thecomputer system (1200).

The core (1240) can include one or more Central Processing Units (CPU)(1241), Graphics Processing Units (GPU) (1242), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1243), hardware accelerators for certain tasks (1244), and so forth.These devices, along with Read-only memory (ROM) (1245), Random-accessmemory (1246), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1247), may be connectedthrough a system bus (1248). In some computer systems, the system bus(1248) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1248),or through a peripheral bus (1249). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1241), GPUs (1242), FPGAs (1243), and accelerators (1244) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1245) or RAM (1246). Transitional data can be also be stored in RAM(1246), whereas permanent data can be stored for example, in theinternal mass storage (1247). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1241), GPU (1242), massstorage (1247), ROM (1245), RAM (1246), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1200), and specifically the core (1240) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1240) that are of non-transitorynature, such as core-internal mass storage (1247) or ROM (1245). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1240). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1240) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1246) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1244)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding a first portion of video data to obtain firstdecoded data corresponding to at least two pictures of a plurality ofpictures, the video data corresponding to the plurality of pictures thatis associated with respective Picture Order Count (POC) numbersindicating a temporal order of the plurality of pictures andrespectively in N temporal layers; allocating M memory spaces, M being apositive integer less than or equal to N; identifying one or morepictures of the at least two pictures for decoding a second portion ofthe video data corresponding to a current picture; in a case that theone or more identified pictures includes two or more identifiedpictures, selecting a collocated reference picture from the two or moreidentified pictures based on one of (i) the POC numbers of the two ormore identified pictures and the current picture, and (ii) a selectionindex provided in the video data; in a case that the one or moreidentified pictures includes only one identified picture, selecting theonly one identified picture as the collocated reference picture;decoding the second portion of the video data using the collocatedreference picture to obtain second decoded data corresponding to thecurrent picture; storing the first decoded data corresponding to the oneor more identified pictures in one or more respective memory spaces ofthe M allocated memory spaces; and in a case that the one or moreidentified pictures includes a particular picture in a same temporallayer as the current picture, at least partially updating data stored inone of the M memory spaces that corresponds to the particular pictureusing the second decoded data corresponding to the current picture. 2.The method of claim 1, wherein, in the case that the one or moreidentified pictures includes the two or more identified pictures, theselecting the collocated reference picture from the two or moreidentified pictures comprises: selecting one of the two or moreidentified pictures that corresponds to a closest POC number differencewith respect to the current picture as the collocated reference picture.3. The method of claim 1, wherein, in the case that the one or moreidentified pictures includes the two or more identified pictures, theselecting the collocated reference picture from the two or moreidentified pictures is performed based on the POC numbers of the two ormore identified pictures and the current picture, comprises: in a casethat two of the two or more identified pictures correspond to a closestPOC number difference with respect to the current picture, performingone of selecting one of the two of the two or more identified picturesin a lowest temporal layer of the identified pictures as the collocatedreference picture, and selecting one of the two of the two or moreidentified pictures in a highest temporal layer of the identifiedpictures as the collocated reference picture.
 4. The method of claim 1,wherein the M memory spaces are associated with M of the N temporallayers, respectively.
 5. The method of claim 4, further comprising:obtaining the positive integer M from the video data.
 6. The method ofclaim 4, further comprising: determining the positive integer M based ona picture size of the plurality of pictures.
 7. The method of claim 4,wherein the positive integer N is greater than two, the positive integerM is less than or equal to the positive integer N, and the M allocatedmemory spaces are associated with M lower temporal layers among the Ntemporal layers.
 8. The method of claim 1, further comprising: in a casethat the one or more identified pictures includes less than M picturesand the current picture is in a lowest temporal layer of the N temporallayers, storing the second decoded data corresponding to the currentpicture in a vacant one of the M memory spaces.
 9. The method of claim8, further comprising: in a case that the one or more identifiedpictures includes M pictures, the one or more identified pictures andthe current picture are in different temporal layers, and the one ormore identified pictures include two pictures in the lowest temporallayer, storing the second decoded data corresponding to the currentpicture in one of the M memory spaces that stores decoded datacorresponding to one of the two pictures in the lowest temporal layerthat has a smallest POC number.
 10. The method of claim 1, wherein theat least partially updating the data stored in the one of the M memoryspaces comprises storing the second decoded data corresponding to thecurrent picture in place of the decoded data corresponding to theparticular picture.
 11. An apparatus, comprising: processing circuitryconfigured to: decode a first portion of video data to obtain firstdecoded data corresponding to at least two pictures of a plurality ofpictures, the video data corresponding to the plurality of pictures thatis associated with respective Picture Order Count (POC) numbersindicating a temporal order of the plurality of pictures andrespectively in N temporal layers; allocate M memory spaces, M being apositive integer less than or equal to N; identify one or more picturesof the at least two pictures for decoding a second portion of the videodata corresponding to a current picture; in a case that the one or moreidentified pictures includes two or more identified pictures, select acollocated reference picture from the two or more identified picturesbased on one of (i) the POC numbers of the two or more identifiedpictures and the current picture, and (ii) a selection index provided inthe video data; in a case that the one or more identified picturesincludes only one identified picture, select the only one identifiedpicture as the collocated reference picture; decode the second portionof the video data using the collocated reference picture to obtainsecond decoded data corresponding to the current picture; store thefirst decoded data corresponding to the one or more identified picturesin one or more respective memory spaces of the M allocated memoryspaces; and in a case that the one or more identified pictures includesa particular picture in a same temporal layer as the current picture, atleast partially update data stored in one of the M memory spaces thatcorresponds to the particular picture using the second decoded datacorresponding to the current picture.
 12. The apparatus of claim 11,wherein the processing circuitry is further configured to: in the casethat the one or more identified pictures includes the two or moreidentified pictures, select one of the two or more identified picturesthat corresponds to a closest POC number difference with respect to thecurrent picture as the collocated reference picture.
 13. The apparatusof claim 11, wherein the processing circuitry is further configured to:in a case that the one or more identified pictures include the two ormore identified pictures, and two of the two or more identified picturescorrespond to a closest POC number difference with respect to thecurrent picture, perform one of selecting one of the two of the two ormore identified pictures in a lowest temporal layer of the identifiedpictures as the collocated reference picture, and selecting one of thetwo of the two or more identified pictures in a highest temporal layerof the identified pictures as the collocated reference picture.
 14. Theapparatus of claim 11, wherein the M memory spaces are associated with Mof the N temporal layers, respectively.
 15. The apparatus of claim 14,wherein the positive integer N is greater than two, the positive integerM is less than or equal to the positive integer N, and the M allocatedmemory spaces are associated with M lower temporal layers among the Ntemporal layers.
 16. The apparatus of claim 11, wherein the processingcircuitry is further configured to: in a case that the one or moreidentified pictures includes less than M pictures and the currentpicture is in a lowest temporal layer of the N temporal layers, storethe second decoded data corresponding to the current picture in a vacantone of the M memory spaces.
 17. The apparatus of claim 16, wherein theprocessing circuitry is further configured to: in a case that the one ormore identified pictures includes M pictures, the one or more identifiedpictures and the current picture are in different temporal layers, andthe one or more identified pictures include two pictures in the lowesttemporal layer, store the second decoded data corresponding to thecurrent picture in one of the M memory spaces that stores decoded datacorresponding to one of the two pictures in the lowest temporal layerthat has a smallest POC number.
 18. A non-transitory computer-readablemedium storing instructions which when executed by a computer for videodecoding causes the computer to perform: decoding a first portion ofvideo data to obtain first decoded data corresponding to at least twopictures of a plurality of pictures, the video data corresponding to theplurality of pictures that is associated with respective Picture OrderCount (POC) numbers indicating a temporal order of the plurality ofpictures and respectively in N temporal layers; allocating M memoryspaces, M being a positive integer less than or equal to N; identifyingone or more pictures of the at least two pictures for decoding a secondportion of the video data corresponding to a current picture; in a casethat the one or more identified pictures include two or more identifiedpictures, selecting a collocated reference picture from the two or moreidentified pictures based on one of (i) the POC numbers of the two ormore identified pictures and the current picture, and (ii) a selectionindex provided in the video data; in a case that the one or moreidentified pictures includes only one identified picture, selecting theonly one identified picture as the collocated reference picture;decoding the second portion of the video data using the collocatedreference picture to obtain second decoded data corresponding to thecurrent picture; storing the first decoded data corresponding to the oneor more identified pictures in one or more respective memory spaces ofthe M allocated memory spaces; and in a case that the one or moreidentified pictures includes a particular picture in a same temporallayer as the current picture, at least partially updating data stored inone of the M memory spaces that corresponds to the particular pictureusing the second decoded data corresponding to the current picture. 19.The non-transitory computer-readable medium of claim 18, wherein the Mmemory spaces are associated with M of the N temporal layers,respectively.